Restart the phone by holding down the power button until it turns off, wait at least 10 seconds and then turn it back on. This should also turn off all apps that are running, if it doesn't, then try turning off all running apps. If it is still not working you may need to have a corrupted cache and or needs a full factory reset, rifer to Samsung Galaxy Prevail 2 Troubleshooting for a detailed guide on those to steps.
First try a different outlet. If the outlet is not the issue, then try using a different charging cable. If the outlet and the charging cable are fine then the micro USB port is probably broken and needs to be replaced. Rifer to Samsung Galaxy Prevail 2 Troubleshooting for more information.
The audio on the phone could be on mute. to fix this go to "Apps->Settings->Sound->Volume" and make sure that all the levels are on the highest setting. Now make sure that there is nothing in the head phone jack, there could be head phones in the jack. If the jack is clear then the problem could be due to a software malfunction, try restarting the phone by holding the power button and waiting 10 seconds before restarting it. If the problem still persists then you'll need to replace the speakers. Rifer to Samsung Galaxy Prevail 2 Troubleshooting for more information.